Apparatus for making curved sandwich panels



April 14, 1964 T. A. HERBERT, JR 3,128,734

APPARATUS FOR MAKING CURVED SANDWICH PANELS Original Filed Jan. 12 19565 Sheets-Sheet 1' as ,2 H I4 /3O ,34 Q 59, ;39 4O 2 a2 14 I0 Q 38 -15 193 32 92 88 86 /1 as 54 94 9/ 87 e5 aw 53 3 E 34 30 3/ I Q9Q9 I3 12 T I089 a 33 I4 o o 4s- 42 3 47 a4 30 2 II INVENTOR.

T A. HERBERT JR.

'5. film ATT NEY April 14, 1964 T. A. HERBERT, JR 3,128,734

APPARATUS FOR MAKING CURVED SANDWICH PANELS Original Filed Jan. 15, 19565 Sheets-Sheet 2 I I I04 FIG. 5

I (66 66,7I INVENTOR 1 MEI m l M Y T. A. HERBERT JR. Kim

ATTORNEY April 14, 1964 T. A. HERBERT, JR

APPARATUS FOR MAKING CURVED SANDWICH PANELS 5 Sheets-Sheet 3 OriginalFiled Jan. 13, 1956 I i I69 INVENTOR.

T. A. HERBERT JR.

2. raw,

FIG.

ATTORNEY Ap 1964 T. A. HERBERT, JR 4 APPARATUS FOR MAKING CURVEDSANDWICH PANELS ori inal Filed Jan. 13, 1956 5 Sheets-Sheet 4 INVENTOR.

T. A. HERBERT JR.

A TTORNE Y April 14, 1964 A. HERBERT, JR 3,123,734

APPARATUS FOR MAKING CURVED SANDWICH PANELS Original Filed Jan. 13, 19565 SheetsSheet 5 INVENTOR.

T A. HERBERT JR.

ATTORNEY FIG. /0

United States Patent 3,128,734 APPARATUS FOR MAKING CURVE!) SANDWICHPANELS Thomas A. Herbert, Jr., Chnla Vista, Calif, assignor to RohrCorporation, a corporation of California Original application Jan. 13,1956, Ser. No. 558,973, now

Patent No. 2,979,005. Divided and this application Mar. 13, 1961, Ser.No. 102,343

Claims. (Cl. 113-99) This invention relates to the construction ofmetallic sandwich structures wherein the ends of a metallic cellularcore are brazed to the opposing faces of two spaced apart metallic skinsand more particularly to an apparatus and method for making metallicsandwich structures having substantially cylindrical or semi-cylindricalshapes.

This application is a division of my copending application for Apparatusfor Making Curved Sandwich Panels, Serial No. 558,973, filed January 13,1956, now Patent No. 2,979,005.

It is a primary object of this invention to provide a method andapparatus for constructing a cylindrical or semi-cylindrical metallicsandwich structure in which the skins and core are held in smoothly andaccurately assembled relationship with each other during the brazingoperation.

A further object is to provide a method and apparatus with which acylindrical or semi-cylindrical sandwich structure may be made havingskins free from wrinkles or other unwanted distortions.

Another object is to provide a method and apparatus in which the skinsand core are pressed together in assembled relationship with an evenlydistributed pressure.

A further object is to provide a method and apparatus for constructing ametallic sandwich structure in which the brazing operation takes placein a non-oxidizing atmosphere.

A still further object is to provide a method and apparatus for making ametallic sandwich structure in which the differential between theco-efiicient of thermal expansion of two metals is used to applypressure to press the skins tightly against the core during the brazingoperation.

A further object is to provide a method and apparatus with whichaccurately shaped cylindrical and semi-cylindrical sandwich structuresmay be made.

Another object is to provide apparatus for the construction of sandwichstructures which is of durable and inexpensive construction.

These and other objects and advantages will become apparent as thedescription of the invention proceeds.

For a better understanding of the invention reference is made to theaccompanying drawing illustrating a preferred embodiment thereof and inwhich:

FIG. 1 is a top view of a cylindrical support on which a cylindricallyshaped metallic sandwich structure is supported,

FIG. 2 is a cross sectional view of FIG. 1 taken on line 2-2,

FIG. 3 is an enlarged sectional view of FIG. 2 taken on line 3-3,

FIG. 4 is an enlarged sectional view of FIG. 1 taken on line 4-4,

FIG. 5 is a schematic view of a furnace and a container in which thesupport is placed during the brazing operation together with a source ofinert gas for providing a nonoxidizing atmosphere,

FIG. 6 is a top view of the container shown in FIG. 5,

FIG. 7 is a cross sectional View of FIG. 6 taken on line 77,

FIG. 8 is a side view of a container in which a support for asemi-cylindrical sandwich structure is placed during the brazingoperation with portions cut away to show details of the construction ofthe container, the support and the sandwich structure,

FIG. 9 is a cross sectional view of FIG. 8 taken on line 99,

FIG. 10 is an enlarged sectional view of FIG. 9 taken on line 10-10,

FIG. 11 is an enlarged view of the end portion of the sandwich structureshown in FIG. 8.

With reference to FIGS. 1 and 2 of the drawing wherein is shownapparatus for supporting a cylindrically shaped sandwich structureduring the brazing operation which includes a tubular member 10 made ofa cylindrically formed sheet of semi-rigid metal on which acylindrically shaped sandwich structure 11 is held by means of aflexible metallic blanket 12. Disposed within member 10 in spaced apartpositions and in frictional engagement with the inner surface 13 ofmember 10 are annular metallic ribs 14 which are preferably T-shaped insection as shown. The ends 15 and 16 of ribs 14 are spaced apart andconnected by connectors 17 and 18 which are positioned on the ends 19and 20 of the projecting portion 21 of ribs 14 (see FIG. 4). Connectors17 and 18 have abutting faces 22 and 23 inclined at an acute angle andin sliding engagement with each other and connector 17 has a projectingportion 24 provided with an opening 25 in which a bolt 26 is rotatablysecured with the axis thereof parallel to faces 22 and 23. Connector 18is provided with a threaded opening 27 in alignment with opening 25 inwhich the extending end 28 of bolt 26 is threadedly engaged. Rotation ofbolt 26 in the proper direction to advance end 28 of bolt 26 intoopening 27 draws connector 18 upwardly with face 23 thereof moving alongface 22 of connector 17 to thus move ends 19 and 20 of rib 14 away fromeach other causing rib 14 to expand and press outwardly against surface13 of member 10. Rotation of bolt 26 in the opposite direction forcesconnector 18 downwardly with face 23 thereof moving along face 22 ofconnector 17 to allow ends 19 and 20 of rib 14 to move toward each otherand reduce the force with which rib 14 presses against surface 13 ofmember 10. VA reinforcing web 29 having a series of spaced apart boltholes 30 along its edge 31 which, when ribs 14 are expanded are inalignment with similarly spaced bolt holes 32 in extending portion 21 ofrib 14, is secured to portion 21 of each of ribs 14 by means of bolts33, to rigidly hold ribs 14 in supporting positions against the innersurface 13 of member 10. Webs 29 are made of sheet metal reinforced byrigid members 34 attached thereto and extending radially outward from acentral opening 35. Webs 29 are provided with openings 36 positionedbetween member 34 and a recess 37 in edge 31 to accommodate connectors17 and 18. A rigid hollow column 38 extends through central opening 35in webs 29 with the upper end 39 thereof extending out past the upperend 40 of member 10 and the lower end 41 thereof extending out past thelower end 42 of member 10. Lower end 41 of column 38 is provided with abase 43 having a body portion 44 surrounding end 41 and an outwardlyextending portion 45, and upper end 39 of column 38 is provided with alifting pin 46 positioned therein. The walls of openings 35 are insliding engagement with column 38 and the inner ends 47 of rigid members34 attached to web 29 positioned at lower end 42 of member 10 engage theupper end 48 of base 43 so that the entire structure is supported andheld upright on column 38.

Tubular member 10, ribs 14, webs 29 and column 38 are all made of ametal having a high coefiicient of thermal expansion and are preferablymade of a stainless steel alloy known commercially as type 316consisting of: Chromium 16 to 18%, nickel 10 to 14%, molybdenum 2 to 3%,manganese 2%, silicon 1% and the balance iron and minor impurities. Thisalloy has a coeflicient of thermal expansion of 10.6)(10- per degreeFahrenheit.

Flexible blanket 12 with which sandwich structure 11 is held inassembled relationship on tubular member is made of relatively thinflexible sheet metal and is sufliciently long to encompass structure 11with its ends 49 and 50 overlapping for a considerable distance. End 49of blanket 12 is tapered as shown in FIG. 1 of the drawing so that end50 passes smoothly thereover permitting blanket 12 to remain in fullcontact with structure 11. Blanket 12 is provided with a series ofspaced apart curved connecting links 51 each of which has one end 52pivotally connected to a bolt 53 which passes through a bracket 54attached to the overlapping end 50. The opposite end 55 of each of links51 is attached to the end 56 of a threaded bolt 57 which extends throughan annular projection 58 attached to blanket 12 near end 50. A threadednut 59 is threadedly engaged with the extending end 60 of bolt 57 sothat by rotating nut 59 link 51 and end 50 of blanket 12 may be drawntoward projection 58 thereby drawing blanket 12 snugly against structure11 and pressing the structure against member 10. Blanket 12 is made of ametal having a low coeflicient of thermal expansion and is preferablymade of a stainless steel alloy known commercially as type 410consisting of: Chromium 11.5 to 13.5%, nickel 0.5% maximum, manganese 1%maximum, silicon 1% maximum and the balance iron and minor impurities.This alloy has a coeflicient of thermal expansion of 6.4x 10".

To provide a non-oxidizing atmosphere in which to perform the brazingoperation the entire supporting apparatus and sandwich structure isplaced within a cylindrical container 61 having a cover 62. The bottom63 of container 61 is provided with a centrally positioned locating plug64 arranged to engage and fit within the lower end 41 of column 38 andan annular support 65 surrounding plug 64 is arranged to engage thelower ends of sandwich structure 11, tubular member 10 and blanket 12. Apair of inlet tubes 66 extend through bottom 63 and are connected to atube 67 for a purpose to be explained. The side wall 68 of container 61is provided with upwardly projecting flanges 69 and 70 secured to theinner and outer surfaces thereof adjacent its upper end 71 form ing apair of annular channels 72 and 73 at end 71. Cover 62 has a centrallypositioned locating plug 74 attached to the upper wall 75 thereof whichis arranged to engage and fit within the upper end 39 of column 38. Apair of outlet tubes 76 extend through wall 75 of cover 62 and areconnected to a tube 77 for a purpose to be explained. The side wall 78of cover 62 has an outwardly and downwardly projecting flange 79 securedto the outer surface thereof adjacent its end 80. Flange 79 and end 80are spaced so that when cover 62 is placed on container 61 flange 79 ispositioned in channel 72 and end 80 is placed in channel 73 to supportcover 62. Channels 72 and 73 are filled with sand shown at 81surrounding end 80 and flange 70 to provide a seal against leakage ofgas therethrough. Container 61 is supported on rails 82 and cover 62 isprovided with bars 83 attached thereto as lifting handles.

8 To use the above described apparatus for holding a sandwich structurein assembled relationship during the brazing operation, webs 29 aredisconnected from ribs 14 by removal of bolts 33 and connectors 17 and18 are adjusted in the manner previously described to permit ends 15 and16 of ribs 14 to move inwardly toward each other allowing ribs 14 tocontract and move away from surface 13 of tubular member 10. Connectors17 and 18 are removed from ends 19 and 20 of portion 21 and ribs 14 andwebs 29 are removed from within tubular member 10. Contraction andremoval of ribs 14 from member 10 permits member 10 to contract so thatits edges (not shown) move toward each other into slightly overlappingpositions. A sheet of quartz glass cloth 84 (see FIG. 3) is then wrappedaround tubular member 10, sheet 84 being of sufficient length so thatits ends overlap an amount equal to the overlap of the edges of member10. Sheet 84 is held in position on member 10 by temporary securingmeans such as adhesive cellulose tape. A thin flexible sheet of metal 85is then wrapped around member 10 over sheet 84, metal sheet 85 being ofsuflicient length to permit the ends thereof to overlap an amount equalto the overlap of the edges of tubular member 10. Sheet 85 is also heldin position around sheet 84 by temporary securing means similar to thatused on sheet 84. The inner skin 86 of sandwich structure 11 is thenwrapped around tubular member 10, skin 86 being of suflicient length sothat its ends overlap a small amount and when its ends are joinedtogether the resulting cylinder has a circumference of the size desired.The ends of skin 86 are connected together in overlapping positions byplacing a strip of brazing alloy foil between the ends and applyingsufficient heat to melt the brazing material after which the ends areallowed to cool thus connecting the ends and holding skin 86 in positionon member 10. Ribs 14 and webs 29 are then placed within member 10around column 38 and connectors 17 and 18 placed on ends 19 and 20 ofprojecting portion 21 of ribs 14. Ribs 14 are positioned in tubularmember 10 in spaced apart positions as shown in FIG. 2 and bolts 26 arerotated to draw connector 18 upwardly moving ends 15 and 16 of ribs 14away from each other thus expanding ribs 14 out against inner surface 13of member 10. The expansion of ribs 14 continues until member 10 hasbeen expanded sufficiently to bring its edges into alignment with eachother which also is sulficient to expand sheet 84 and metal sheet 85 tobring the overlapping ends thereof into alignment with each other. Theexpansion of member 10 as above described presses the sheet of quartzglass cloth 84 and metal skin 85 outwardly against the inner surface ofskin 86 which, having its ends connected together, cannot expand so thatit becomes tautly drawn around member 10 over sheets 84 and 85. Anyforce exerted by the expansion of ribs 14 and member 10 in excess ofthat required to draw skin 86 taut is prevented from injuring skin 86 bythe compressibility of sheet 84 which acts as a cushion between skin 86and tubular member 10. When ribs 14 have been expanded sufficiently webs29 are secured to projecting portions 21 of ribs 14 by means of bolts 33as shown in FIG. 2 with inner ends 47 of members 34 on web 29 positionedat lower end 42 of member 10 resting on upper end 48 of base 43. Theouter surface of skin 86 is then covered with a thin sheet of brazingalloy 87 which is secured to skin 86 by spot soldering at spaced apartpoints. The brazing alloy is a known type and the thickness of the sheetmay vary with the amount of brazing material deposit desired in thefinished article. In brazing the ends of a cellular core made ofstainless steel approximately .002 of an inch in thickness to the facesof skins made of stainless steel approximately .010 of an inch inthickness, it has been determined that a sheet of brazing alloyapproximately .002 of an inch thick consisting of 85% silver and 15%manganese placed between the ends of the core and the faces of skinswill provide a suitable bond between the core and skins when heated toabout 1800 F. A suitable end supporting member such as a channel or Z-shaped in section bar (not shown) as is customarily used to form theedges of metallic sandwich panels and which has been formed to conformto the shape of skin 86, is placed on the brazing alloy sheet 87 alongeach of the ends of skin 86. The edge members are secured in position byspot brazing them at spaced intervals to skin 86. A metallic cellularcore 88, preferably of the type having walls 89 provided with openings90 is then wrapped around skin 86 over brazing alloy sheet 87. Core 88is wrapped snugly and smoothly around skin 86 with its edges disposed inclosely abutting positions and its sides in contact with the edgesupporting members. The abutting edges of core 88 are connected togetherby brazing and core 88 is held in position by being spot brazed to skin86 at spaced intervals. A sheet of brazing alloy91 similar to brazingalloy sheet 87, is placed over the outer surfaces of core 88 and theedge members, sheet 91 being held in position by being spot brazed tocore 88 at spaced apart intervals. The outer skin 92 of structure 11 isthen wrapped around core 88 and the edge supporting members over brazingalloy sheet 91. Skin 92 is drawn smoothly and tightly around core 88with its ends overlapping a small amount. A strip of brazing materialsimilar to sheet 91 is placed between the overlapping ends of skin 92and the ends spot brazed together to hold skin 92 tightly wrapped aroundcore 88. Skin 92 is also spot brazed to the face of core 88 to hold theskin in position. A thin flexible sheet of metal 93 similar to sheet 85is wrapped around skin 92 and secured in position thereon with temporary securing means such as adhesive cellulose tape. A sheet of quartzglass cloth 94 similar to sheet 84 is wrapped around sheet 93 andsecured in position therearound with temporary securing means such asadhesive cellulose tape. Blanket 12 is then wrapped around sheet 94 andsecured therearonnd by connecting ends 49 and 50 thereof together bymeans of links 51 and the blanket drawn tightly around the entirestructure in the manner previously described, to press the abovedescribed assembly against tubular member 10 and hold skin 86, core 88and skin 92 in assembled position for performing the brazing operation.

The entire supporting structure and sandwich structure are then placedin container 61 with lower end 41 of column 38 surrounding plug 64,collar 45 resting on bottom 63, and the lower ends of sandwich structure11, tubular member 10 and blanket 12 resting on annular sup port 65.Cover 62 is placed on container 61 with end 80 of wall 78 and flange 79positioned in channels 72 and 73 as previously described and plug 74engaged within upper end 39 of column 38. The entire supportingstructure and sandwich position within container 61 by engagement ofplugs 74 and 64 with upper and lower ends 39 and 41 of column 38 and theweight of the tubular member 10, sandwich structure 11 and blanket 12 issupported by annular support 65 to prevent a downward force beingapplied to webs 29 during the brazing operation.

Container 61 containing the entire supporting apparatus and sandwichstructure 11 as above described is placed within a furnace 95 (see FIG.having walls 96 containing an electrical heating element 97 the ends 98and 99 of which are connected to a source of electrical current (notshown). Walls 96 of furnace 95 are provided with an opening 100extending therethrough and through which tubes 101 and 102 pass. Tube101 is connected to tube 77 which is connected to outlet tubes 76 incover 62 and tube 102 is connected to tube 67 which is connected toinlet tubes 66 in bottom 63 of container 61. Tube 102 has a portion 103formed as a helical coil disposed within furnace 95 and is connected toa source 104 of pressurized inert gas, preferably argon, through a valve105. To perform the brazing operation valve 105 is opened to permitargon gas to flow slowly through tubes 102 and 67 and inlets 66 intocontainer 61. The argon gas being heavier than air, forces the airwithin container 61, including the air in sandwich structure 11,upwardly and out through outlets 76 in cover 62 and out through tubes 77and 1. When container 61 is completely filled with gas and all airtherein has been forced out, electrical current is directed into heatingelement 97 to raise the temperature of the furnace atmosphere, Thefurnace temperature is raised to a degree at which the brazing alloydisposed between core 88 and skins 86 and 92 is melted which, when thealloy described is used, is at about 1800 F. While the furnace isheating and during the time required to heat the sandwich structure, asmall amount of argon gas is permitted to flow into container 61 and thegas within the container displaced thereby is permitted to escapethrough outlets 76 and tubes 77 and 101. The gas admitted to container61 is heated prior to entering the container by passing through coiledportion 103 of tube 102 disposed within structure 11 are held in a fixedfurnace 95. As the temperature within container 61 rises tubular member10, webs 29, ribs 14 and column 38, being made of metal having a highcoefiicient of thermal expansion, expands a substantial amount pressingskin 86, core 88 and skin 92 outwardly against blanket 12 which beingmade of metal having a low coetlicient of thermal expansion, expands arelatively small amount. The pressure thus applied presses skins 86 and92 and sheets of brazing alloy 87 and 91 tightly against core 88. Thepressure applied in this manner is prevented from damaging skins 86 and92 and core 88 by the cushioning efl ect of quartz glass cloth sheets 84and 94 disposed on each side of the skins and core. When the temperaturein furnace 95 is sufliciently high to melt the brazing alloy containedin the above described assembled structure, the flow of electricalcurrent to element 97 is stopped and the entire apparatus and structureis allowed to cool sufiiciently so that the brazing alloy may harden andbond the parts of the assembled structure together. Valve is closed andtubes 101 and 102 are disconnected from tubes 77 and 67 and container 61is removed from the furnace. Cover 62 is removed from container 61 andthe entire supporting apparatus and sandwich structure supported thereonare lifted out of the container. Blanket 12 and quartz glass sheet 94are removed from around the sandwich structure and bolts 33 removeddisconnecting webs 29 from ribs 14. Connectors 17 and 18 are adjusted topermit ends 15 and 16 of ribs 14 to move toward each other and allowtubular member 10 to contract. The assembled sandwich structure 11 isthen removed from tubular member 10 by being lifted upwardly over end 40thereof. Flexible metal sheets 85 and 93 are then removed from skins 86and 92 and the brazing operation is complete. The adhesive cellulosetape used as temporary securing means in the above described process isgenerally completely consumed by the heat to which the assembly issubjected during the brazing operation and the parts on which it wasused are unaffected thereby.

With reference to FIGS. 8 and 9 of the drawing wherein apparatus isshown for supporting a semi-cylindrically shaped sandwich structure 106during the brazing operation which includes a semi-cylindrically shapedrigid metallic shell 107 comprising an inner curved plate 108 supportedby horizontally and vertically disposed interconnected webs 109. Plate108 is provided with spaced apart openings 110 extending therethroughand is coveredby a similarly shaped plate 111 on which the sandwichstructure 106 is supported. Webs 109 have edges 112 shaped to engage theinner surface 113 of plate 108 and are secured to a plate 114 in a knownmanner such as by welding. Plate 114 is secured to a standard 115 bymeans of bolts 116 and standard 115 is secured to a base plate 117 bymeans of bolts 118. Base plate 117 is supported by a series of spacedapart rails 119 to which plate 117 is secured by bolts 120. Webs 109 areprovided with spaced apart openings 121 extending therethrough andcentrally aligned openings 122 through which a hollow rigid column 123extends with the marginal walls of openings 122 secured to column 123 asby welding to provide the assembled webs with additional rigidity.

Sandwich structure 106 is held in assembled position during the brazingoperation within a flexible metallic envelope 124 which is constructedin a manner and for a purpose to be explained. Envelope 124 andstructure 106 are held in position against shell 107 by a flexiblemetallic blanket 125 of suflieient size to completely cover envelope124. The depending ends 126 of blanket 1 25 are cut at intervals asindicated at 127 and the portions are formed into slings 128 into whichweights 129* such as metal bars are placed to draw blanket 125downwardly pressing envelope 124 and sandwich structure 106 againstshell 107. Attached to base plate 117 and extending the length thereofare rails 130 having inclined faces 131 sloping inwardly toward eachother. Slings 128 containing weights 129 are engaged by faces 131 andurged inwardly toward each other so that the force with which blanket125 is drawn downwardly against envelope 124 and sandwich structure 106is evenly distributed over the entire surface of structure 106.

Envelope 124 is provided with an inlet tube 132 (see FIG. 11) extendingalong one end of sandwich structure 106 and connected to a tube 133 andan outlet tube (not shown) extending along the opposite end of sandwichstructure 106 and connected to a tube 134 for a purpose to be explained.

The supporting apparatus and sandwich structure are covered with a metalcover 135 which rests on base plate 117 in sealing engagement therewith.Cover 135 has a curved body portion .136 provided with stitfeners 137and end walls 138. Body 136 and ends 138 have an outwardly anddownwardly projecting flange 139 secured thereto which is spaced awayfrom and parallel to the edges 140 thereof. Base plate 117 is providedwith a pair of channels 141 and 142 extending therearound arranged toreceive flange 139 and edges 1 40 which are formed by a pair of flanges143 and 144 similar to flange 139 and which are secured to oppositesides of an upright member 145 attached to base plate 117. Channels 141and 142 are filled with sand as indicated at 146 to seal the channelsagainst leakage of gas therethrough. To permit tubes 133 and 134 toextend outside of cover 135, edge 140 and flange 139 are provided withnotches 147 (see FIG. of sufficient size to permit the tubes to passtherethrough and upright member 145 is provided with a slot 148 (seeFIG. 9) arranged to permit the tubes. to pass therethrough. Tubes 133and 134 extend downwardly into channel 141 through sand 146 and acrossthrough notches 147 and slot 148 and out through channel 142. Base plate117 is provided with an inlet 1'49 opening into cover 135 and cover 135is provided with an outlet 150 for a purpose to be explained. Cover 135and base plate 117 are both provided with suitable lifting pads 151 tofacilitate lifting and moving the apparatus.

To use the above described apparatus for holding the parts of asemi-cyclindrically shaped sandwich structure in assembled relationshipduring the brazing operation the sandwich structure is first assembledin the following manner. On a metal sheet 152 (see FIG. 11) the area ofwhich is equal to the area of sandwich structure 106, is placed a sheetof quartz glass cloth 153. On sheet 153 is placed a thin metal sheet 154of the same size and shape as sheet 153 and on sheet 154 is placed askin 155 of structure 106. A sheet of brazing alloy 156 similar tosheets of brazing alloy 87 and 91 previously described, is placed onskin 155. A metallic cellular core 157 similar in construction to core88 and provided with vents 90 extending through the walls 89 thereof, isplaced on brazing alloy sheet 156. A second sheet of brazing alloy 158similar to sheet 156 is placed on core 157 on which the second skin 159of structure 106 is placed. A thin sheet of metal 160 similar to sheet154 is placed on skin 159 and a sheet of quartz glass cloth 161 similarto sheet 153 is placed on metal sheet 160. A metal sheet 162 similar tometal sheet 152 is placed on quartz glass sheet 161. In assembling theparts of sandwich structure 106 as above described, suitable edgesupporting members such as the channel or Z shaped members previouslymentioned may be placed around core 157 between sheets of brazing alloy156 and 158 and skins 155 and 159 to provide suitable edge supportingmeans for sandwich structure 106. The above described assembly is placedon a thin sheet of flexible metal 163 which is of substantially greaterarea than sandwich structure 106 and having outwardly projecting edges164. A thin sheet of flexible sheet metal 165 equal in size to sheet 163is placed on the assembly with its edges 166 projecting out over edges164 of sheet 163. Inlet tube 132 and the outlet tube (not shown) arepositioned along core 157 and the extending edges 164 and 166 of sheets163 and 165 are secured together as indicated at 167 to form envelope124 surrounding the entire assembly. Sheet 165 is provided with suitableopenings 168 through which tubes 133 and 134 pass for connection withthe inlet and outlet tubes Within envelope 124. Envelope 124 containingsandwich structure 106 assembled as described, is then placed on shell107 and blanket is placed thereon. To provide means for positioningenvelope 124 and blanket 125 properly on shell 107 one of the edges ofblanket 125 and envelope 124 are each provided with a notch (not shown)the marginal walls of which engage a locating pin 169 positioned in anopening 170 adjacent one end of shell 107, when blanket 125 and envelope124 are properly placed on shell 107. Weights 129 are then placed inslings 128 and the slings positioned against faces 131 of rails so thatblanket 125 is drawn downwardly and inwardly pressing envelope 124 andthe entire assembly contained therein smoothly and evenly against shell107. Cover is then placed on base plate 117 over the entire supportingapparatus in the manner previously described and the entire structure isplaced in furnace 95. Tube 102 is then connected to inlet 149 in baseplate 117 and tube 101 is connected to outlet in cover 135. Tubes 133and 134 are extended out through opening 100 in wall 96 and tube 133 isconnected to a source of inert gas (not shown) and tube 134 is connectedto an aspirator of a known type (not shown). The area surrounding thesupporting apparatus between base plate 117 and cover 135 is filled withinert gas, preferably argon, in the same manner that container 61 isfilled. Vacuum is applied to tube 134 to withdraw air from withinenvelope 124 to reduce the pressure therein to below the pressure of thesurrounding atmosphere. Inert gas is then admitted into envelope 124through tube 133 at a controlled rate which permits the pressure withinenvelope 124 to remain below the pressure of the surrounding atmosphere.When the area surrounding the supporting apparatus is filled with gasand the air has been entirely withdrawn from Within envelope 124 andreplaced with an inert gas at a pressure below the pressure of thesurrounding atmosphere, electrical current is directed into heatingelement 97 to heat the furnace atmosphere to a temperature sufficient tomelt the brazing alloy. The gas within envelope 124 provides anonoxidizing atmosphere in which the brazing operation takes place and,being at a reduced pressure, causes sheets 163 and 165 to be pressedinwardly by the surrounding atmosphere to apply additional pressurepressing sheets of brazing alloy 156 and 158 and skins and 159 inwardlyagainst core 157 to assure a firm contact between the skins and core asthe brazing alloy is melted. The inert gas surrounding the entiresupporting apparatus prevents deterioration of the apparatus due tooxidation when it is subjected to the high temperatures within thefurnace. When the temperature within furnace 95 is sufliciently high tomelt the brazing alloy the flow of electrical current to heating element97 is stopped and the entire structure is allowed to cool so that thebrazing alloy may harden and bond the ends of core 157 to skins 155 and159. Withdrawal of gas from envelope 124 through tube 134 and admissionof gas into envelope 124 through tube 133 is stopped. The admission ofgas through inlet 149 is stopped and tubes 101 and 102 disconnected fromoutlet 150 and inlet 149. Tubes 133 and 134 are removed from opening 100and the entire apparatus is removed from furnace 95. Cover 135 isremoved from base plate 117 and blanket 125 is removed from aroundenvelope 124. The envelope is then opened and sandwich structure 106removed therefrom. The sheets of metal and quartz glass cloth previouslydescribed are removed from the structure and the brazing operation iscomplete.

The skins and cores used in the construction of the sandwich structuresherein described are preferably made of a stainless steel alloy althoughother types of metal may be used. The cores are preferably made of metalapproximately .002 of an inch in thickness and the skins made of sheetmetal approximately .010 of an inch or less in thickness so that theparts are sufiiciently flexible to be easily shaped as described.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present embodiment of the invention is therefore to beconsidered as in all respects illustrative and not restrictive, thescope of the invention beind indicated by the appended claims, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

Having thus described my invention, What I claim as new and useful anddesire to secure by Letters Patent is:

1. In the construction of a metallic sandwich structure having a closedcylindrical shape wherein the ends of a metallic cellular core arebrazed to the opposed faces of two spaced apart cylindrically shapedmetallic skins, means for holding said skins and core in assembledrelationship during the brazing operation comprising: a tubular membercomprising a semi-rigid sheet of metal formed end to end into asubstantially cylindrical shape adapted to support said skins and core;a plurality of circumferentially expansible and adjustable annular splitrings disposed within said tubular member, said split rings respectivelyhaving inwardly extending annular ribs, said rings being expanded toengage the inner surface of said tubular member and to adjustably expandand hold said member in a desired shape; a plurality of disc shapedsupporting webs disposed within said tubular member, said webs beingsecured to and arranged to engage and hold said annular ribs in fixedpositions and each of said webs being provided with a central opening; arigid hollow column passing through said central openings and inengagement with the marginal walls thereof, the ends of said columnextending out past the ends of said tubular member; and a flexiblemetallic blanket surrounding said sandwich structure and pressing saidskins and core together and against said tubular member.

2. Apparatus as claimed in claim 1; in which said tubular member,supporting rings, supporting webs and hollow column are composed of ametal having a coefiicient of thermal expansion of predetermined valueand said blanket is composed of a metal having a coefli- 10 cient ofthermal expansion less than said predetermined value.

3. In the construction of a metallic sandwich structure having a closedcylindrical shape wherein the ends of a metallic cellular core arebrazed to the opposed faces of two spaced apart cylindrically shapedmetallic skins, means for holding said skins and core in assembledrelationship during the brazing operation comprising: a tubular membercomprising a semi-rigid sheet of metal formed end to end into asubstantially cylindrical shape adapted to support said skins and corein assembled relationship; a plurality of adjustable circumferentiallyexpansible annular split rings disposed within said tubular member inspaced apart positions, said split rings being expanded to engage theinner surface of said member and to adjustably expand and hold saidtubular member in a desired shape, said split rings respectively havinginwardly extending annular ribs; a plurality of disc shaped supportingwebs disposed within said tubular member, said webs being secured to andarranged to engage and hold said annular ribs in fixed positions andeach of said webs being provided with a central opening extendingtherethrough; a hollow rigid column passing through said centralopenings and in engagement with the marginal walls thereof, the ends ofsaid column extending out past the ends of said tubular member; aflexible metallic blanket surrounding said sandwich structure andpressing said skins and core together and against said tubular member;and a closed container arranged to contain said supporting means, saidskins and core and a mass of inert gas.

4. Apparatus as claimed in claim 3; in which said container is providedwith inlet and outlet openings.

5. Apparatus as claimed in claim 3; in which the ends of said containerare provided with means arranged to engage the extending ends of saidn'gid column.

References Cited in the file of this patent UNITED STATES PATENTS2,155,705 Gottwald Apr. 25, 1939 2,609,311 Engler Sept. 2, 19522,860,673 Rauseo Nov. 18, 1958 2,944,504 Herman et a1. July 12, 19603,071,853 Price et al Ian. 8, 1963

1. IN THE CONSTRUCTION OF A METALLIC SANDWICH STRUCTURE HAVING A CLOSEDCYLINDRICAL SHAPE WHEREIN THE ENDS OF A METALLIC CELLULAR CORE AREBRAZED TO THE OPPOSED FACES OF TWO SPACED APART CYLINDRICALLY SHAPEDMETALLIC SKINS, MEANS FOR HOLDING SAID SKINS AND CORE IN ASSEMBLEDRELATIONSHIP DURING THE BRAZING OPERATION COMPRISING: A TUBULAR MEMBERCOMPRISING A SEMI-RIGID SHEET OF METAL FORMED END TO END INTO ASUBSTANTIALLY CYLINDRICAL SHAPE ADAPTED TO SUPPORT SAID SKINS AND CORE;A PLURALITY OF CIRCUMFERENTIALLY EXPANSIBLE AND ADJUSTABLE ANNULAR SPLITRINGS DISPOSED WITHIN SAID TUBULAR MEMBER, SAID SPLIT RINGS RESPECTIVELYHAVING INWARDLY EXTENDING ANNULAR RIBS, SAID RINGS BEING EXPANDED TOENGAGE THE INNER SURFACE OF SAID TUBULAR MEMBER AND TO ADJUSTABLY EXPANDAND HOLD SAID MEMBER IN A DESIRED SHAPE; A PLURALITY OF DISC SHAPEDSUPPORTING WEBS DISPOSED WITHIN SAID TUBULAR MEMBER, SAID WEBS BEINGSECURED TO AND ARRANGED TO ENGAGE AND HOLD SAID ANNULAR RIBS IN FIXEDPOSITIONS AND EACH OF SAID WEBS BEING PROVIDED WITH A CENTRAL OPENING; ARIGID HOLLOW COLUMN PASSING THROUGH SAID CENTRAL OPENINGS AND INENGAGEMENT WITH THE MARGINAL WALLS THEREOF, THE ENDS OF SAID COLUMNEXTENDING OUT PAST THE ENDS OF SAID TUBULAR MEMBER; AND A FLEXIBLEMETALLIC BLANKET SURROUNDING SAID SANDWICH STRUCTURE AND PRESSING SAIDSKINS AND CORE TOGETHER AND AGAINST SAID TUBULAR MEMBER.